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Discussion Starter · #1 ·
i have a oddly shaped, small bed room(around 15x10 or so) that i would like to add acoustic panels to. i want a really perfect listening area. i want the bass to sound the same everywhere in the room(with proper sub placement of course) and minimum sound reflection. id be willing to post pics of my room if it is needed for one of you to give proper advice. i could even make a replica of it in google sketch up.



now, just an average question...

in order for a bass trap to work well, does it have to be placed in a corner? can you just put foam in every corner of your room?
 

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Assuming you mean porous absorber bass traps (insulation or mineral fiber boards), the most effective locations are where the standing waves are at minimum pressure - maximum velocity. This is generally 1/4 of a wavelength from a boundary. That's a really bad spot if you want to occupy the room at the same time as the absorber.
For reference, a 100Hz wave is more than 10ft long - so the position of optimal absorption is about 2.5 ft away from the wall. Your 10ft wide room just got cut in half.


Each standing wave reflects off boundaries in a predictable pattern - the most troubling standing waves reflecting off parallel surfaces - walls or floor and ceiling. A standing wave will be established between each set of parallel surfaces when excited with the right frequencies, so in theory you would want to absorb the particular frequency of sound that produces a standing wave as it reflects from one of the walls. So, quickly, your mind jumps ahead a few steps and you begin to visualize a room with absorbers on all the surfaces. This is the beginnings of building an anechoic chamber, and you don't want that (plus, you'd never get there, even if you thought you wanted that). So where's the middle ground? For most people, the corners is a good compromise, because an absorber in a corner is absorbing sound reflected off two walls - not just one. Plus, being in the corner, it uses less important floor space. With that in mind, consider other corners you're not using - like the corner formed by the ceiling and wall.


So, bass traps actually don't work "best" in the corners, but they do the most work, per unit volume, in the corners.


The question you didn't ask though, is "should I use foam?" And the answer there is "no." Especially at very low frequencies, below say, 80 to 100 Hz I think, very loose fiberglass insulation is the best absorber (buy rolls or batts of the stuff you would place in your walls). For other bass - say up to 300 Hz (I think), you'll do better with rigid panels of mineral fiber, such as Owens Corning's product number 703 or 705 (OC703, or OC705, as often abbreviated in these forums).


For minimizing seat-to-seat variation, multiple subs is critical. They need not be large and expensive, but there should be several - three is usually a great number, but two is greatly improved over one.


Fred
 

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Discussion Starter · #3 ·
thanks. i already have 2 subs. so ill get another better one to be like the "main" and the other two will cover the spots where im not sitting so other people when they are watching movies with me will have the same experience.


any tips on building the fiberglass panels?
 
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